The invention relates to a full-face mask for use with Non-Invasive Positive Pressure Ventilation (NIPPV), Continuous Positive Airway Pressure (CPAP) and ventilators generally.
The delivery of a supply of breathable gas at positive pressure to a patient from a ventilator requires some sort of interface between machine and patient. An endo-tracheal tube is typically used as a patient interface in invasive ventilation. In non-invasive ventilation, some form of mask is used as a patient interface.
A mask typically comprises a chamber having a nose-receiving cavity defined by a shell or frame. The mask typically further comprises a comfortable face-contacting portion, such as a cushion, which may be secured to an edge of the shell or frame. Masks are typically held in position on a patients face using an arrangement of headgear, such as a set of elastic straps. It is a continuing challenge for mask designers to improve the comfort of masks, particularly where the mask has to be worn for many hours.
Unless a mask is constructed for each user, because of the wide variety of shapes, most designs of masks represent a compromise. One design of mask might be a good fit for a sub-group of patients with one shape of nose (e.g., with a high nasal bridge), but poorly fit another sub-group with a different shape of nose (e.g., with a low nasal bridge). It can be particularly difficult to design a mask which provides a good seal in the nasal bridge region because that region of the face is particularly sensitive.
Folds and creases in the mask cushion can become very uncomfortable on a patient's face with prolonged wear. Furthermore, in spite of the use of a cushion, the edge of a mask frame can be felt through the cushion and present an uncomfortable surface to the patient's face, particularly if the cushion is compressed.
In some cases it is appropriate for a mask to include a vent which amongst other things can allow a controlled leak flow of gas from the mask to prevent a build up of CO2 within the mask. There may also be inadvertent or unintentional leak from the mask, for example, at a junction between the mask and the patient's skin. The functioning of sophisticated control algorithms in ventilators, particularly those responding to a respiratory flow signal, is improved with the use of a mask which provides low or zero unintentional leak flow.
Patients move during sleep. In addition, the shape of their head can change during sleep, due to, for example, swelling. While a mask may fit a patient well when initially fitted, because of such movement, the mask may not fit well later in the night. Prior art masks typically include elastic headgear straps that can be shortened or stretched or otherwise rearranged on the head to return the mask to a comfortable low-leak position.
The level of pressure support provided by the ventilator can vary during the course of treatment. Some Continuous Positive Airway Pressure (CPAP) devices provide an initial ramp from a low pressure up to a therapeutic pressure. Other CPAP devices automatically adjust the pressure in accordance with indications of flow limitations. Other devices vary the level of pressure support within a respiratory cycle of the patient, for example, by providing a higher level during inhalation and a lower level during exhalation. Elastic headgear straps must be arranged to suit the level of pressure. If the elastic straps are arranged to suit a high pressure level, there is a risk that the straps will be too tight and uncomfortable for a low pressure level.